sgr-agent

Pure Rust LLM client and agent framework based on Schema-Guided Reasoning (SGR) by Rinat Abdullin. No dlopen, no external binaries. Works on iOS, Android, WASM — anywhere reqwest + rustls compiles.

Two layers

Layer 1 — LLM Client (default features: gemini, openai): structured output, function calling, flexible parsing. Just add a dependency and call an API.

Layer 2 — Agent Framework (feature: agent): Tool trait, registry, agent loop with loop detection, 4 agent variants, dual-model routing, retry, streaming. Build autonomous agents that reason and act.

Quick start

# Cargo.toml

# Client only (structured output + function calling)
sgr-agent = "0.2"

# Full agent framework
sgr-agent = { version = "0.2", features = ["agent"] }

Structured output (client only)

use sgr_agent::gemini::GeminiClient;
use sgr_agent::ProviderConfig;
use schemars::JsonSchema;
use serde::Deserialize;

#[derive(JsonSchema, Deserialize)]
struct Recipe {
    name: String,
    ingredients: Vec<String>,
    steps: Vec<String>,
}

#[tokio::main]
async fn main() {
    let client = GeminiClient::new(
        ProviderConfig::gemini("YOUR_API_KEY", "gemini-3.1-pro-preview")
    );

    let response = client
        .structured::<Recipe>(&[("user", "Give me a pasta recipe")], None)
        .await
        .unwrap();

    println!("{}: {} steps", response.output.name, response.output.steps.len());
}

Agent with tools

use sgr_agent::agent_loop::{run_loop, LoopConfig, LoopEvent};
use sgr_agent::agent_tool::{Tool, ToolError, ToolOutput};
use sgr_agent::agents::sgr::SgrAgent;
use sgr_agent::context::AgentContext;
use sgr_agent::gemini::GeminiClient;
use sgr_agent::registry::ToolRegistry;
use sgr_agent::types::Message;
use sgr_agent::ProviderConfig;
use serde_json::Value;

struct ReadFile;

#[async_trait::async_trait]
impl Tool for ReadFile {
    fn name(&self) -> &str { "read_file" }
    fn description(&self) -> &str { "Read a file from disk" }
    fn parameters_schema(&self) -> Value {
        serde_json::json!({
            "type": "object",
            "properties": {
                "path": { "type": "string", "description": "File path to read" }
            },
            "required": ["path"]
        })
    }
    async fn execute(&self, args: Value, _ctx: &mut AgentContext) -> Result<ToolOutput, ToolError> {
        let path = args["path"].as_str().ok_or(ToolError::InvalidArgs("missing path".into()))?;
        match std::fs::read_to_string(path) {
            Ok(content) => Ok(ToolOutput::text(content)),
            Err(e) => Ok(ToolOutput::text(format!("Error: {e}"))),
        }
    }
}

struct Finish;

#[async_trait::async_trait]
impl Tool for Finish {
    fn name(&self) -> &str { "finish_task" }
    fn description(&self) -> &str { "Call when the task is complete" }
    fn is_system(&self) -> bool { true }
    fn parameters_schema(&self) -> Value {
        serde_json::json!({
            "type": "object",
            "properties": {
                "summary": { "type": "string" }
            },
            "required": ["summary"]
        })
    }
    async fn execute(&self, args: Value, _: &mut AgentContext) -> Result<ToolOutput, ToolError> {
        Ok(ToolOutput::done(args["summary"].as_str().unwrap_or("Done")))
    }
}

#[tokio::main]
async fn main() {
    let client = GeminiClient::new(
        ProviderConfig::gemini("YOUR_API_KEY", "gemini-3.1-pro-preview")
    );

    let tools = ToolRegistry::new()
        .register(ReadFile)
        .register(Finish);

    let agent = SgrAgent::new(client, "You are a coding assistant.");

    let mut ctx = AgentContext::new();
    let mut messages = vec![Message::user("Read main.rs and summarize it")];
    let config = LoopConfig { max_steps: 10, ..Default::default() };

    run_loop(&agent, &tools, &mut ctx, &mut messages, &config, |event| {
        match event {
            LoopEvent::StepStart { step } => eprintln!("step {step}"),
            LoopEvent::ToolResult { name, output } => {
                eprintln!("  {name} -> {}...", &output[..output.len().min(100)]);
            }
            LoopEvent::Completed { steps } => eprintln!("done in {steps} steps"),
            _ => {}
        }
    }).await.unwrap();
}

Features

Architecture

LLM Client layer

Agent Framework layer (feature = "agent")

Agent variants

SgrAgent (structured output)

Best for capable models (Gemini 3.1 Pro, GPT-4o). Builds a discriminated union JSON Schema from your tools at runtime, sends via structured_call, parses response with flexible parser + coercion.

let agent = SgrAgent::new(client, "You are a helpful assistant.");

ToolCallingAgent (native function calling)

Simplest variant. Sends tools via native FC API, gets Vec<ToolCall> back directly. Works with any model that supports function calling.

let agent = ToolCallingAgent::new(client, "You are a helpful assistant.");

FlexibleAgent (text parsing)

For weak models or text-only backends (Ollama, local models). Puts tool descriptions in the system prompt as human-readable text, parses JSON from model's free-form response. Includes retry with error feedback.

let agent = FlexibleAgent::new(client, "You are a helpful assistant.");

HybridAgent (2-phase reasoning)

Two-phase approach: Phase 1 calls a "reasoning" tool only (think step), Phase 2 sends the full toolkit with reasoning context. Best for complex multi-step tasks.

let agent = HybridAgent::new(client, "You are a helpful assistant.");

PlanningAgent (read-only plan mode)

Wraps any agent to restrict tools to a read-only subset. The agent explores the codebase, then calls submit_plan with a structured plan. Like Claude Code's plan mode.

use sgr_agent::agents::planning::{PlanningAgent, Plan};
use sgr_agent::agents::clarification::{ClarificationTool, PlanTool};

let inner = SgrAgent::new(client, "You are an architect. Analyze and create an implementation plan.");
let planner = PlanningAgent::new(Box::new(inner));

let tools = ToolRegistry::new()
    .register(ReadFile)
    .register(ListDir)
    .register(SearchCode)
    .register(PlanTool)           // submit_plan — produces structured Plan
    .register(ClarificationTool); // ask_user — pause for questions

run_loop(&planner, &tools, &mut ctx, &mut messages, &config, |_| {}).await?;

// Extract the plan after completion
let plan = Plan::from_context(&ctx).unwrap();
println!("{}", plan.summary);
for (i, step) in plan.steps.iter().enumerate() {
    println!("{}. {} (files: {:?})", i + 1, step.description, step.files);
}

// Inject plan into build agent's context
let plan_msg = plan.to_message();
build_messages.insert(1, plan_msg);

Interactive agents (clarification)

Use run_loop_interactive when the agent may need to ask the user questions:

use sgr_agent::agent_loop::run_loop_interactive;
use sgr_agent::agents::clarification::ClarificationTool;

let tools = ToolRegistry::new()
    .register(ReadFile)
    .register(WriteFile)
    .register(ClarificationTool) // ask_user tool
    .register(Finish);

// Async callback — called when agent needs user input
run_loop_interactive(
    &agent, &tools, &mut ctx, &mut messages, &config,
    |event| { /* handle events */ },
    |question| async move {
        println!("Agent asks: {}", question);
        // Get user input (from stdin, GUI, API, etc.)
        let mut input = String::new();
        std::io::stdin().read_line(&mut input).unwrap();
        input.trim().to_string()
    },
).await?;

The regular run_loop also supports WaitingForInput events but continues with a placeholder instead of pausing.

Dual-model routing

Use a smart model for complex decisions and a fast model for simple ones:

use sgr_agent::router::{ModelRouter, RouterConfig};

let router = ModelRouter::new(
    GeminiClient::new(ProviderConfig::gemini(&key, "gemini-3.1-pro-preview")),
    GeminiClient::new(ProviderConfig::gemini(&key, "gemini-3.1-flash-lite-preview")),
).with_config(RouterConfig {
    message_threshold: 10,  // use smart when < 10 messages
    tool_threshold: 8,      // use smart when < 8 tools
    always_smart: false,
});

// Use router as any LlmClient — routing is transparent
let agent = SgrAgent::new(router, "You are a helpful assistant.");

Retry with backoff

Wrap any client with automatic retry on transient errors (rate limits, 5xx, timeouts):

use sgr_agent::retry::{RetryClient, RetryConfig};

let client = RetryClient::new(GeminiClient::new(config))
    .with_config(RetryConfig {
        max_retries: 3,
        base_delay_ms: 500,
        max_delay_ms: 30_000,
    });

Honors Retry-After headers from rate limit responses.

Agent loop

The loop drives the agent: decide → execute tools → feed results back → repeat.

use sgr_agent::agent_loop::{run_loop, LoopConfig};

let config = LoopConfig {
    max_steps: 50,              // hard limit on iterations
    loop_abort_threshold: 6,    // abort after 6 consecutive identical actions
    max_messages: 80,           // sliding window — trim old messages
    auto_complete_threshold: 3, // auto-complete if situation repeats 3x
};

let steps = run_loop(&agent, &tools, &mut ctx, &mut messages, &config, |event| {
    // handle events: StepStart, Decision, ToolResult, Completed, LoopDetected, Error
}).await?;

3-tier loop detection:

1. Exact signature — same tool call sequence repeats N times
2. Tool frequency — single tool dominates >90% of all calls
3. Output stagnation — tool outputs are identical across steps

Auto-completion detection:

• Catches agents that finished but forgot to call finish_task
• Keyword detection ("task is complete", "all done", etc.)
• Repeated situation text (agent stuck describing same state)

Sliding window:

• Keeps first 2 messages (system + user prompt) + last N
• Inserts a summary marker where messages were trimmed

Agent lifecycle hooks

Override hooks on the Agent trait for cross-cutting concerns:

impl Agent for MyAgent {
    async fn decide(&self, messages: &[Message], tools: &ToolRegistry) -> Result<Decision, AgentError> {
        // your decision logic
    }

    fn prepare_context(&self, ctx: &mut AgentContext, messages: &[Message]) {
        // inject context before each decision (e.g., update working state)
    }

    fn prepare_tools(&self, ctx: &AgentContext, tools: &ToolRegistry) -> Vec<String> {
        // filter/reorder tools based on context (return tool names to include)
        tools.list().iter().map(|t| t.name().to_string()).collect()
    }

    fn after_action(&self, ctx: &mut AgentContext, tool_name: &str, output: &str) {
        // post-action hook (e.g., log, update state, track changes)
    }
}

Vertex AI

let config = ProviderConfig::vertex(
    "ACCESS_TOKEN",           // from `gcloud auth print-access-token`
    "my-gcp-project",
    "gemini-3.1-pro-preview",
);
// Default region: "global" (aiplatform.googleapis.com)

Flexible parser

The flexible parser extracts JSON from messy LLM output — markdown blocks, broken JSON, streaming chunks, chain-of-thought wrapping:

use sgr_agent::{parse_flexible, parse_flexible_coerced};
use schemars::JsonSchema;
use serde::Deserialize;

#[derive(JsonSchema, Deserialize)]
struct Output { answer: String }

// Handles: ```json {...} ```, bare JSON, broken brackets, single quotes, trailing commas
let result: Output = parse_flexible_coerced(
    r#"Here's my answer: ```json {"answer": "42"} ```"#,
    &schema,
)?;

Progressive discovery

Filter tools by relevance when you have many tools but want to show only the most relevant ones:

use sgr_agent::discovery::ToolFilter;

let filter = ToolFilter::new(5); // show max 5 tools
let relevant = filter.select("read the config file", &registry);
// Returns: system tools (always) + top-scored tools by keyword overlap

Running the example

A full 15-tool coding agent demo is included:

# With Google AI
export GEMINI_API_KEY=your_key
cargo run -p sgr-agent --features agent --example agent_demo -- "Create a hello world Python script"

# With Vertex AI
export GOOGLE_CLOUD_PROJECT=my-project
cargo run -p sgr-agent --features agent --example agent_demo -- "Create a hello world Python script"

The example includes: ReadFile, WriteFile, EditFile, ListDir, Bash (with 30s timeout), BackgroundTask, SearchCode, Grep, Glob, GitDiff, GitStatus, GitLog, GetCwd, ChangeDir, FinishTask.

Standalone project example

# Cargo.toml
[package]
name = "my-agent"
version = "0.1.0"
edition = "2021"

[dependencies]
sgr-agent = { version = "0.2", features = ["agent", "gemini"] }
serde_json = "1"
tokio = { version = "1", features = ["rt-multi-thread", "macros"] }
async-trait = "0.1"

See /tmp/my-agent for a full working standalone project.

License

MIT